The difference between fault fast and fault safe in Java

Serial number	Key	Unsatisfactory	Fault-tolerant
1	Exception	Any changes to the collection (such as adding, deleting, and updating the collection during a thread) will fail when iterating over the collection and then quickly throw a concurrent modification exception.	Fault-tolerant collections do not throw exceptions.
2.	Collection types	ArrayList and hashmap collections are examples of quick-failure iterators	CopyOnWrite and concurrent modification are examples of fault-tolerant iterators
3.	Performance and memory	but works on the actual set. Therefore, this iterator does not require additional memory or time	It is processing a clone of the set, not the actual set. There is an overhead in terms of time and memory
4.	Modification item	Iterators do not allow modification of the set while iterating over it.	Fail-safe iterators allow modifications to be made to the collection while iterating over it.

Fail-Fast Example

public class FailSafeExample{
　　　public static void main(String[] args){
　　　　　　ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<String, Integer>();
　　　　　　//Add elements to the map
　　　　　　map.put("Dell",　1;
　　　　　　map.put("IBM",　2;
　　　　　　//Get iterator from the map
　　　　　　Iterator<String> it = map.keySet().iterator();
　　　　　　while (it.hasNext()){
　　　　　　String key = (String) it.next();
　　　　　　　　　System.out.println(key+" : "+map.get(key));
　　　　　　　　　map.put("Google",　3;
　　　　　　}
　　　}
}

Output Result

IBM :2
Dell:1

Fail-Fast Example

public class FailFastExample{
　　　public static void main(String[] args){
　　　　　　List<Integer> list = new ArrayList<Integer>();
　　　　　　list.add(1;
　　　　　　list.add(2;
　　　　　　list.add(3;
　　　　　　//Get iterator from the list
　　　　　　Iterator<Integer> it = list.iterator();
　　　　　　while (it.hasNext()){
　　　　　　　　　Integer integer = (Integer) it.next();
　　　　　　　　　list.add(4;
　　　　　　}
　　　}
}

Output Result

Exception in thread "main" java.util.ConcurrentModificationException
　　　at java.util.ArrayList$Itr.checkForComodification(Unknown Source)

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